Arunprabhu Arunachalam Sugumaran¹, Ryan Bower², Ming Fu², David Owen¹, Papken Hovsepian¹, Peter Petrov², Rupert Oulton², Thomas Smith¹, Arutiun P. Ehiasarian^1
1Sheffield Hallam University, Sheffield, United Kingdom
²Imperial College London, London, United Kingdom
Plasmonic catalysis enabled by visible light is vital to enhancing the ability of surfaces to enable a broad range of chemical reactions including water splitting and associated production of bioactive reactive oxygen species. However standard catalysts that rely on nanoparticles are not sufficiently robust for deployment in the environment. Transition metal nitrides are promising candidates whose functionality is influenced on their purity and structure. High-Power Impulse Magnetron Sputtering has been deployed to tailor the texture and morphology of nanoscale multilayer TiN / NbN coatings and evaluate the effect on their robustness and plasmonic activity. Plasma characterisation shows a significant fraction of dissociated nitrogen and double-charged metal ions in both TiN and NbN deposition conditions. Time-resolved ion energy distribution functions obtained from energy-resolved mass spectroscopy indicate that 30% of atomic nitrogen possesses a high-energy tail and originates from sputtering from the target surface alongside Ti and Nb, thereby increasing adatom mobility and intergranular density and promoting a strong (200) fibre texture as observed in XRD pole figures. The native oxides on the coating surface analysed by XPS showed that the presence of Nb promoted significant increases in the lifetime of active electron species in the films due to trapping of hot carriers in oxygen vacancies such as Nb³⁺. The bi-layer thickness in nanoscale multilayer films was used to design films with a large grain size as determined by AFM, and increased hardness and toughness as determined from nanoindentation. Ellipsometric measurements of the real component of the dielectric permittivity confirmed an excellent plasmonic activity. The effects of carrier lifetime on photocatalytic activity are discussed. The results pave the way to using nanoscale multilayer coatings for catalysis.